Worm Gear Clamps What you need to know
Worm gear stainless steel band style clamps are found in a wide range of applications ranging from the radiator hose on your 2018 Corvette or F150 Ford truck up to large 12 or 16 inch diameter clamps used on duct work and dust collection systems. At first glance an in-depth discussion about the mechanics and characteristics of stainless steel gear drive band clamps could seem like a subject that could put you to sleep. However, a good knowledge of how clamps operate how they are made and how they should be applied can be very useful.
The first thing you need to examine is the raw material that the clamp is made from. Typically, all gear style clamps with a worm drive are made from stainless steel. Stainless steel in itself is a rather complicated topic. Clamps are typically made from grade 301 up through grade 316 with grades 304 and 316 being the most common. Most people fail to realize that there’s more than one type of stainless steel. There are numerous classes of stainless steel and within each class there are numerous grades each having a specific set of characteristics which make it applicable to a certain range of applications which is the reason number 304 and Number 316 are used in stainless steel clamps. Many people think that it’s common knowledge that a magnet will not attract stainless steel. Actually, nothing could be further from the truth. When stainless steel is first formed at the mill it is relatively soft and is not suitable for many applications and that particular stainless steel will not be magnetically attractive. However, to make the stainless steel stronger and harder so it can be used in an application such as a band clamp it must be cold worked. This means it must be rolled down and thinned through rollers. This is pretty much equivalent to the process of forging, but it’s done much slower and much more deliberately and with less pressure however, the result in the molecular realignment is very similar. This results in a stainless steel band that is hard, strong, and malleable but has slight magnetic attractive capacities. The part of the clamp you really must pay attention to regarding magnetic attraction is the worm screw. When you think about it it’s really silly to have a high quality stainless steel clamp with a zinc plated carbon steel screw which does not share the same anti corrosive characteristics as the band when in reality the additional cost of having a stainless steel screw is minimal. This is where the magnet comes into play because you can easily test which clamp has the steel screw or stainless steel screw as the magnetic attraction is substantially different.
The basic stainless steel gear clamp consists of three parts the first part being the band, the second part is the housing that the screw goes into which is welded to the band and then the screw. Many people think, incorrectly, that when the housing for the screw is welded to the band the welding process sensitizes the stainless steel in the housing and the band and causes it to be more receptive to corrosion. Studies confirm that this is definitely not the case. When the screw housing is welded to the clamp it’s typically done with 4 spot welds with each weld lasting about one quarter of a second with 1.0 seconds total welding time, and therefore heat exposure time, of about one second or less. Laboratory testing has proven that to intentionally sensitize stainless steel, which means to reduce its corrosion resisting capabilities the steel has to be heated at between 800 and 1250 Fahrenheit for between 1 and 2 hours. Clearly the one second or less weld time to fix the housing to the band falls far short of this.
It’s important to have a clamp that’s appropriately sized to the application it needs to handle. In this context it’s always best to use a clamp size that’s closest to the diameter that it needs to clamp. Using a large clamp for a small diameter application is not a good idea because first it leaves a long tail and the tail can interfere with adjacent activities such as belts, fans, and other moving parts. In addition, it presents a potential point of injury in that it’s easy to get cut, particularly if the band is cut short and the ends are not properly chamfered and filed down to provide a surface that is not conducive to causing cutting injuries. In addition, you will also note that in many instances it does not apply uniform force around the perimeter of the application. On the other hand, using multiple small clamps that are ganged together can be advantageous when applying them to a larger application. For example, if you have a 12 inch diameter application it’s appropriate to use 4 x 3 inch diameter clamps. This will provide four points of pressure that can be independently adjusted around the application to provide much more uniform pressure and therefore a better seal. For this example, we used the three inch stainless steel clamps manufactured by Tech Team https://techteamproducts.com/ their part number 727 Thttps://www.amazon.com/Tech-Team-Band-Style-Key-Style-Collection/dp/B07GZZ1KHV/ref=sr_1_1?ie=UTF8&qid=1550509162&sr=8-1&keywords=tech+team+clamp. These are high quality clamps made to close tolerances and do the job exceedingly well. Just to see how they might apply it’s simply a matter of doing the math. Each 3 inch diameter clamp has a band length of 9.5 inches and a 12 inch diameter clamp has a band length that is not surprisingly exactly four times that. So you can see how the four smaller clamps linked together can actually make a far superior connection.
Finally, there’s always the question of should the gear mechanism and screw of the clamp be lubricated. Generally speaking clamps with zinc plated steel screws have somewhat of a lubrication function built into the zinc plating. As the screws engage the plating shears off in minute amounts and this provides a lubricating function. On clamps with stainless steel screws it’s a good idea to put some motorcycle chain wax, WD 40, or a small drop of Singer sewing machine oil on the screw mechanism. The reason is that this will help maintain the performance level of the clamp and if the clamp needs to be reused at any time will allow the effective disengagement of the worm screw and allow the clamp to perform at its specified level.