There are 2 type of Chemical (resin) Mine Roof Support Bolts:
Non-Tension Bolts, which are long rods (average length 5’), ribbed all along, with a forged square head.
The ribs are used to mix the resin. The head with a plate washer underneath are supporting the mine roof, without tensioning it.
Tension Rebar, which are long Bolts, ribbed along the bar except the end which is threaded. The ribs are used for mixing the resins and the thread is used for supporting the mine roof, by tensioning a nut once the resin has cured. This product is more complex and more expensive.
The Tension Rebar are made from ribbed (deformed) bar, which is peeled or swaged at the end to the pitch diameter of the thread. Then, the end is thread rolled in a separate operation.
The patented Videx process is using pitch diameter bars, which save at least 4% in material cost; The bars are ribbed by cold rolling to achieve higher strength and a better adhesion to the resins. The ribbing process is extending the bars by an average of 9%.
The Videx line is comprised of the following equipment:
Ø Bar feeder with a 5 ton cradle, that can handle big bundles.
Ø Automatic ribbing machine, which is receiving the bars one at a time, and is ribbing the requested length, leaving the bar with no ribs at the end where the thread will be rolled.
Ø Transfer system, receiving the ribbed bars from the ribbing machine, and feeding them into a horizontal planetary thread roller.
Main features of Videx patented process:
Ø The rod diameter is the pitch diameter of the thread that will be rolled on it.
Ø The cut-to-length blanks are fed fully automatically to the dimpling machine which indents dimples or ribs over its entire length except some 150mm at the end, which are left blank, for thread rolling.
Ø The dimpled blanks are being straightened by a dual-plane roller straightener and are automatically transferred to the thread rolling machine which rolls the thread over the 150mm at the end of the blank.
Types of Bolts that can be made on the Videx line:
These bars have dimples on the sides, which are good in mixing the resin.
This pattern is most suitable for medium carbon steels like 1040-1045 and for smaller diameters like M16 (5/8”) to M20 (3/4”).
Modified auxiliary indented for better load transfer. Very good in mixing the resin. Suitable for high tensile materials and for bigger diameters; M-20 & M-24.
This is a combined form, with impressions that yield increased effective external diameter. The increased diameter results in a better load transfer capability.
Advantages of the Videx process in production of Mine Roof Supporting Bolts:
Ø Thread rolling is performed directly on the hot rolled material without the need to shave the ribs. The process is faster, with no dirt or scrap.
Ø The whole process is made fully automatically, supervised by one operator. The wire speed is 25 meter/minute.
Ø Less steel is required because the bar is stretched during the process of indenting the ribs.
Ø The ribbing process is not influencing the yield and ultimate strength of the material.
The current process for 3/4” and 7/8” tensioned requires use of rods with a diameter under the ribs larger then the pitch diameter by at least 0.3mm.
The saving in material using pitch diameter is at least more then 4%.
The ribbing process is extending the bars by 9%. This is a pure saving of 9% in material cost.
The total saving in material cost is at least 13%, without affecting the yield and ultimate strength required.
The Videx Ribbing (VRB) line is capable of rolling 25 meter/minute, or 1,500 meter/hour. In 10 hours the theoretic production is15,000 meters.
The practical average production is 4,000-6,000 bars/day. Each bar is 1.8m long (about 6’), so the length processed every day is 7,200 to 10,800 meter. Assuming that the average daily production is 5,000 bars, the line is producing each day 9,000 kg. The daily saving in material cost is 13% of 9,000 kg, which is 1,170 kg, or 2,580 lb. The monthly saving (20 working days) is over50,000 lbs.
In addition to the saving in material cost the production is fully automatic, requiring less labor. The efficiency of the process is determined mostly by the material buying price, and of course the ability to sell as many rebar as the machine can make.