Power Sweeper Broom Engineering 101
Make smarter replacement decisions
by Roy Hedstrom
by knowing brooms from the inside out.
No matter what type of mechanical sweeper you operate, one of the most critical factors affecting its performance over the long-run is the quality of the normal replacement parts which are used on it. This article addresses how to evaluate the brooms, which are one of the most important components as far as mechanical sweepers are concerned.
Before competing brooms can be evaluated, it may be helpful to know what types of main brooms are available. In the U.S. there are several different types of brooms in use. Interestingly, some brooms that are still in use today use pretty much the same technology as when street sweepers were first invented.
Brooms that were cable-wrapped were one of the first type used by sweepers. These brooms were first put onto street sweeping machines in the late teens and early twenties, at which time the brooms themselves were made of palmyra, a wood fiber. It wasn't until after World War II that brooms underwent their first basic change; that is when polypropylene started being used as filament material. The cable-wrapped broom is one where the core contains channels, or steel wraps. Today, about 100 lbs of polypropylene is wrapped with cable around a core. They are still made by hand.
There are many sweepers across the country that are still using this system. Increasingly, it is becoming less or non-cost-effective since the entire core must be removed and sent to a remote location to be stripped and re-wrapped. Besides the extra shipping costs, storage is also a consideration because shops must maintain a supply of cores.
After World War II another broom system, the wafer-type, started competing for a share of the market. Wafer brooms have a core system onto which individual segments are fitted. Although the core must still be removed from the sweeper, the wafer system makes it easier. At first, these wafers were 'flat' and needed spacers. Within the last 10 or so years a new system, called the 'convoluted' wafer, has been invented. The new wafers are bent so that no spacers are necessary. The filaments for the wafers are made of poly or wire, and this type of broom is widely available.
The wafer-type system is most prevalent within the road broom industry. The road broom industry is significantly different from the street sweeper industry because street sweepers usually have a hopper, or containing system, for the debris to be picked up. Road broom systems windrow the debris off the road, and are normally not used in situations where there are curbs.
About 20 years ago, the Milwaukee Dustless Brush Company introduced a tube-broom system. Its biggest innovation was its compression-type core. With a tube-broom, what used to be a two or three hour broom changing operation for an experienced mechanic was reduced to 30 to 45 minutes. Plus it's not as back-breaking: the core weighs only 75 to 120 lbs (depending on the sweeper), whereas the cable-wrap broom cores went up to 200 pounds. Another potential advantage of the tube broom is that they can be double wrapped. More on this later, but for organizations that want to minimize broom change-outs this can be a real advantage.
Milwaukee Dustless Brush Company was responsible for another innovation about five years ago. This was the introduction of what is called a tuft-sweep broom. It is an adaptation of the strip broom that was first developed in the sixties. The tufted type of broom has been used for many years on snow removal equipment for airports and runways. The problem has always been that the bristles had to be installed by hand, which made them costly. They also couldn't be built as strong as needed for a street sweeping application. The majority of street sweeper brooms turn at 120 rpms, and some are up to 200. They also need more downpressure, in order to get a sweeping pattern 4 to 6 inches wide. This translates into a tremendous amount of pressure on both the core and the ends of the polypropylene bristles.
The new tuft-sweep process eliminates having to hand insert bristles by using a technology which actually melts the polypropylene around a steel strip. This is mounted into a mandrel that can be used over the compression core of an existing tube-type broom. Tuft-sweep brooms use the same amount of polypropylene by weight as a standard street sweeping tube broom. These are the options that are available in today's street sweeping broom market.
The evaluation of replacement brooms typically revolves around three factors; quality, price and availability. It's not so much the price of a broom, as what kind of service will be received at that price. Availability also needs to be added to any buying decision, because downtime is such an expense.The combination of these should be thought of as a particular broom's cost-effectiveness, or long-run cost. The rest of the article will introduce and discuss factors which can be used in the evaluation process to choose between the available types of brooms. The best situation is to get a quality product at a fair price, and the intent of this article is to help those who do the purchasing to make the decision for their companies or municipalities.
Everyone that is a buyer of brooms for their organization should know what the OEM specifications are for the broom that came on their sweeper. This information is probably in the Operator's Manual that came with the sweeper. If it isn't, call your dealer or manufacturer and find out the following: who makes the broom; what type it is (cable-wrapped, wafer, tube, tuft-sweep, etc.); what type of steel is in the mandrel (core) and what its weight is; and how many pounds of broom material are in it (poly, steel or combination). That's the only way to develop a standard against which to judge other brooms you may consider. Keep track of how much wear you get on any broom you buy so that way your supplier will be able to help you.
There are plenty of options out there for brooms. I want to offer a couple of considerations to anyone who tends to always choose the lowest priced replacement items possible, whether brooms, bearings or whatever. One is to consider the effect that any replacement parts might have on your warranty. The other is to recognize what effect a substandard part might have on any other parts of the sweeper with which it interacts, as well as how they may affect its operation. Brooms aren't necessarily going to affect another part on the machine, but brooms that aren't up to specification can certainly make the sweeper operate in a different manner.
Any broom you consider should be specified to contain a certain amount of materials. This combination will definitely affect the sweeping performance of the broom. You can pretty much take it as a certainty that if you buy a broom with fewer materials than your OEM quality broom you will reduce your average number of hours of wear (or miles of usage) as well as the sweeping performance. A small reduction in the amount of poly (or other materials) in a broom can be tempting. Less wraps means less poly, channeling and cable to wrap that broom. Therefore it is a lower cost broom initially, but that often is just initial purchase price, not long-run cost.
Unfortunately, we haven't been able to directly relate the performance of a broom to the poundage of bristle material. My guess is, however, that if you reduce the amount of materials used by 10 or 15% you could have a 30 to 50% reduction in the amount of performance of that broom. An example of this disproportionate wear ratio is found in what is termed as 'double-wrapping.' A double-wrapped tube broom doesn't have double the amount of materials in it, but, in many cases, double the amount of work will be gotten from the broom.
Most manufacturers will send you the specifications for what materials are used in their brooms. These should include the weight of both the core and the bristle material, as well as the specifications of the bristles. Unfortunately, I have seen some instances where the purchasing people would have been well served by policing the brooms to make sure that the published weights are the same as the product they are receiving. The simple way to do this is to check the total broom weight by putting it on a scale. The person doing the buying should make it their responsibility to make sure they are getting the specifications they have requested.
Another factor to be aware of is how polypropylene, the bristle material, is manufactured. It is made by extruding a liquid poly around what is called a 'blow-hole.' By going through a nozzle and over this blow-hole, it will then form the size specifications that the manufacturer wants. Although cheaper polypropylene can be made where the outside dimensions can be maintained, the blow-hole will be substantially larger. Typical outside dimensions are usually accepted to be about 78 thousandth of an inch by 108 thousandth of an inch. A large blow-hole will leave the bristles with that dimensional quality on the outside, but the weight of the polypropylene will be less because there is a larger air hole inside it.
Let's compare the length of service between two brooms with the same amount of poly, by weight, but where one uses poly with a large blow-hole. Because it has a larger hole, each bristle won't have as much weight. As a result, to end up with the same total weight there would have to be more bristles added to that broom. The problem is, the bristles with the larger blow-hole will each be more brittle, and will fray faster. Even though there are more of them, service life will be less than on the broom with fewer, but more serviceable, bristles. Unfortunately, on this topic I don't know of any way to tell users what to request. It's just something to look for when comparing competing products. It's a way that buyers can be fooled into a lesser service product.
It's important to know the factors and options, but information from other users of your brand of sweeper is also good to gather. Municipal agencies share this type of information. They aren't in a competitive situation and will usually let you talk with whoever handles purchasing of replacement parts for them. Be sure to ask them to explain why they are using a specific product. Find out if it's because they actually have experienced better sweeping performance and lower operating costs with it.
Suppliers should also be able to help you choose the type of broom you should be using in a particular application. That's why I always want to know what the sweeper is going to sweep. Your supplier is the person in the best position to know what is best for various applications. That's part of the advantage of buying from someone who knows their own product line and also the sweeper user's needs.
In actual use, the type of broom used is very much an individual preference. If you think that all the broom types will perform equally well for you, however, then consider the labor needed to change them out. Typically, a cable-wrapped broom takes longest to change, then a tube-broom, and quickest is a strip broom. The big advantage to strip-type brooms, in most cases, is that the core of the broom does not have to be removed from the equipment, and so that makes it a much faster replacement. It doesn't necessarily even have to be done in the shop. By the same rule of thumb, a double-wrapped tube broom will need to be changed out less often, is less than twice the cost, and as a result often represents a good bargain.
In the future, I expect to see changes which use some of the new materials that are coming along, as well as in the way that the current materials are utilized. For example, poly orientation has received relatively recent attention. Tube-brooms have the polypropylene oriented so that the .108 inch dimension is going in the forward direction. With a strip brush it happens that the .078 inch dimension of the polypropylene is what is facing in the forward direction. On the newer tuft-type of strip broom, the orientation is in every direction. This seems to reinforce the strength of each bristle of the tufts, which is an example of a change that I think the market will support. In the long run, that's what determines what products will remain. I hope that by considering the information in this article, users will be able to make their own purchasing decisions in a more informed manner.
Roy Hedstrom at one time was a Marketing Manager for Elgin Sweeper Company. He holds a bachelor's degree in marketing, and is also a certified professional consultant. For the past 6 and 1/2 years Roy has been president of RLH, Inc., a wholesaler of brooms to the U.S. power sweeping industry. RLH is the marketing representative for Milwaukee Dustless Brush Company, a well known national broom manufacturer. To reach him, call 1-800-332-4505.
This article is reprinted from American Sweeper magazine, v3n3.